SYNCHRONIZED CLOCKS AND MEDIA PLAYERS

Abstract: A media player and the clock which controls it are integrated into a single object. This integration may be achieved by the construct of inheritance between objects in an object oriented programming environment. A software class for player objects is established which inherits from a software class for clock objects. In this way, a player "is a" clock. This integration provides improved synchronization among different media, and simplifies design of applications which employ player objects and clock objects. Each object is synchronized to a RootClock object which operates at the speed of the fastest media player in the system. The RootClock may be separated into "low" order and "high" order components and a compare register in order to reduce interrupt overhead.

Description: SYNCHRONIZED CLOCKS AND MEDIA PLAYERS Cross References The present invention is related to copending, commonly assigned U.S. patent application serial no. xx/xxx-xxx entitled "Event Qualification and Notification" (Attorney Docket no. 55378.0026), and copending, commonly assigned U.S. patent application serial no. yy/yyy,yyy entitled "Time- Based Script Sequences" (Attorney Docket no. 55378.0027), both of which are incorporated by reference herein. Background The present invention relates to the field of multimedia methods and apparatus, and more particularly to methods and apparatus allowing for synchronization and control of time-based media in a multimedia computer environment. With regard to modern computer systems, the term multimedia is often used in referring to software for processing (e.g., creating, editing, displaying, synchronizing, etc.) one or more files of time-based data. Examples of time-based data include video sequences, audio sequences, time- recorded events such as data from measuring devices, etc. Devices (hardware or software) capable of processing multimedia data are commonly referred to as multimedia players. Typical examples include personal computers and custom CD ROM-based devices designed for such a purpose. The time-based data is typically stored in (or on) a hardware memory device, for example the read¬ only memory (ROM) of a computer, a computer's magnetic disk drive, an audio or ROM compact disk (CD) , video tape devices, etc. The time-based data may also be generated for processing in real time. For example, computer-generated animation image data may be generated for display from animation control data, without having previously been stored. The type of data is its "media." That is, media defines the data. For example, digital data is comprised of the binary values 0 or 1. In order to interpret that data, a player must know which media is represented by that data. Hence, devices (principally software) capable of processing the data provided by these hardware memory devices are commonly referred to aε media players. A movie is a common metaphor used in the discussion of multimedia software and hardware. While the traditional "movie" (e.g., of the type shown in a theater) is a stream of discrete data, in time order, stored in a single format such as film, tape, optical disk, etc., multimedia "movies" need not be so organized. Rather, multimedia movies may be made up of a number of sequences whose data may be stored on disparate devices in non-sequential order. Thus, one important role for multimedia players is to organize and coordinate the processing of data. Authors of multimedia movies (or "titles") need to control and synchronize a variety of time- based multimedia components or "players," such as audio and video streams, animation sequences, time- based scripts and full-motion movies. Rather than require the author of each application to maintain complete control over these components, many computer operating systems now include "extensions" which provide higher-level abstractions (such as clock objects and associated media "player" objects) to simplify the author's task. Examples of such systems include "Multimedia Extensions" to the Windows 3.1 operating system environment for IBM-compatible personal computers, from Microsoft Corporation, Redmond, Washington, and the "QuickTime" extension to the Apple Macintosh System 7.x system software, from Apple Computer, Inc., of Cupertino, California. QuickTime is described in detail in the QuickTime Developer's Guide, also available from Apple Computer, Inc., and which is incorporated by reference herein. QuickTime essentially allows a multimedia player to process time-based data. Since the data are time based, QuickTime provides for the description of "time" (called time basis) for the data as well as a definition of the context for evaluating that "time." In QuickTime, a movie's or media's time basis is called its "timebase." A timebase is essentially a vector that defines the direction and velocity of time for a movie or media. The context for a timebase is called its time coordinate system. Conceptually, a time coordinate system provides an axis for measuring time. The time coordinate system, like a geometrical axis, is divided into units of measurement by a measurement system, called a time scale. A timebase defines a current time value and the rate at which time passes for the movie or the media, but does not define the scale. Rather, the scale is obtained from the media itself. The product of rate and the time scale is called the absolute rate, and is measured for example in units per second. Although timebases exist independent of any specific coordinate system, time values extracted from a timebase are meaningless without a time scale. Associated with each timebase is a clock which provides the timing for the timebase. QuickTime clocks are implemented as components that are managed by a part of the QuickTime architecture referred to as the Component Manager. Clock components provide two basic services: generating time information and scheduling time-based events, called CallBack events. For a description of event management, see, e.g., the copending commonly assigned U.S. Patent Application, serial number XX/XXX,XXX, entitled "Event Qualification and Notification," which is incorporated by reference herein. Clock components themselves receive information from other elements, which they use to produce and to provide their timing information. For example, a clock component may use the Macintosh "tick" count to provide its basic timing information. Alternatively, a clock component could use some special hardware installed in the computer to provide its basic timing information. In any event, the clock component ultimately derives its timing information from a hardware clock, either directly or indirectly. A hardware clock is generally a signal generator of the type known in the art, which emits pulses or clock "ticks" many times per second (e.g., a 1 MHz clock ticks one million times per second) . Hardware clocks are frequently associated with "counters" that keep track of units of time by incrementing their value after each clock tick of a given rate. While hardware clocks generally emit a predetermined, fixed number of ticks per second, software clocks such as clock components allow for the manipulation of various aspects or values of the clock, allowing control of rate, etc. For example, many computer systems employ a single hardware "root clock" (and an associated counter) , which is typically used aε a baεe to which various software clocks, such as clock componentε, are synchronized. These software clocks must convert the time units of the RootClock (e.g., 60 tickε/sec) to their desired time units (e.g., 44,100 ticks/sec for CD-quality audio). Both media and movies have timebases. In QuickTime, multimedia movies are comprised of one or more "tracks" which are organized references to the media from which the time-based data are obtained. Each track is associated with a single media. A movie's timebase allows the tracks to be synchronized. In QuickTime, every track begins at the same time, at the beginning of the movie. In order to "start" the data of the track at some time other than the beginning of the movie, the data are "offset" from the start of the movie. By starting each track at the same time, one aspect of synchronizing the various tracks is addreεεed. Each track or media haε its own timebase. Every timebase contains a rate, a start time, a stop time, a current time, and some status information. Although ultimately each timebase obtains its time values from a clock component, it may do εo indirectly. A timebase may obtain its i time values directly from another timebaεe. The timebase obtaining its time values from another timebase is referred to as a slave timebase, and the timebase providing time values to other timebaεeε iε referred to aε a maεter timebaεe. A i maεter timebaεe may have multiple slave timebases, but a slave timebase may have only a single master timebase. (That is, a clock can be synchronized to only one clock, but can have any number of clockε synchronized to it.) As an example, a first media may be a stream of digitized video data, and a second media may be a stream of digitized sound data. It may be desirable to "play" the sound at a specific time in the video data stream, such as 10 εeconds into the video data stream. Thus, it is useful to be able to tie one media's timebase to another media's timebase. QuickTime provides for the creation, use, and editing of timebase values. To support the value of tying one media's timebase to another media's timebase, changes made to master timebaεes may ripple through to slave timebases. For example, if the current time of a master timebase is changed, the current time of the slave timebases are changed appropriately. However, changes to timebase values do not ripple up. That is, if the current time of a slave timebaεe is changed, the offset between the movie start time and the data start time is changed, but the current time of the master timebase is not changed. It will thus be appreciated that QuickTime provides an effective mechanism for controlling and synchronizing different media, despite each media having its own timebase with its own rate and offset. However, it will be appreciated that the mechanism provided by QuickTime for the synchronization of the various media iε alεo quite complex, principally because the media and itε associated timebase are conceptually different. In order to access or change the time values associated with a particular media, the timebase for the media, not the media itself, must be addreεεed. For example, to find out at what point in time the media is currently playing, it is necessary to obtain a reference to the media's timebase, then examine the timebase itself. This problem, of requiring indirect access to a player's time parameters, is compounded as the number of players synchronized to one another increases. Furthermore, QuickTime requires that a movie start at time zero. This makes the task of synchronizing two movies that start at different times (i.e., each having a different zero time relative to each other) complex. For example, since a multimedia movie must start at time zero, no negative start times are allowed. While it is possible to achieve the effect of a negative start time in QuickTime, for example by creating a fictitious start time and using offεetε from that start time, this is an unnecesεary burden in the creation of multimedia movies. Not only must the offset between the two movies be maintained, posεible different rateε between the two movieε muεt also be synchronized. These same complexities also occur when a movie is synchronized with some external media. Finally, the timebases discuεεed above do not include scale. The values of time returned by a timebase are meaninglesε without a εcale. To determine the value of time returned by a timebase, reference must be made to the media. This two-step proceεε of getting a timebases' time imposes an arbitrary complexity upon an author of a title. Moreover, the scheduling of future events (e.g., requeεting notification when the audio player is "x" time units into the playback of a particular audio passage) is frequently inaccurate. If, as is often the case, • the root clock does not operate as fast as a clock associated with a particular media player, then the system cannot accurately determine when the audio passage is at a particular point in time. For example, if the root clock operates at 60 ticks/second, and the clock controlling the audio playback operates at 44,100 ticks/εecond, then the system cannot determine when the audio playback reaches audio time unit 100. A total of 735 audio time units pass between every tick of the root clock. Typically, such systems access a faster clock on the computer and approximate the point at which the desired time unit is reached. The problem is that this faεter clock iε not synchronized to the media player, and therefore is not necesεarily accurate (due to the "drift" cauεed by the time taken to write to a counter) . Summary of the Invention The present invention addresses the problems noted above by integrating, both physically and conceptually, media players and the clocks that control them. This system-level integration of clocks and media players provides more accurate synchronization among different media and relieves the author of having to communicate indirectly with multiple clocks and media players, and having to maintain artificial intermediate constructs to facilitate such peripheral activities. Thiε integration between clocks and media iε achieved by the construct of inheritance between objects in an object oriented programming environment. That is, clocks and media players are integrated by creating a class of media player objects that inherits from a class of clock objectε. In object oriented parlance, inεtead of a player "has a" clock relationship between a player object and a clock object, a player "iε a" clock. In thiε manner, all attributes of a clock (e.g., its rate, time, etc.) are inherited by the media player objects conceptually associated with that clock. Thus, direct communication with a media player is facilitated, for example, to obtain the player's current time or to set its time, rate or its offset to a master clock. The concept of "origin" is introduced in the class definitions to provide for the start of a media at an arbitrary point in time. The origin defines the beginning of the media. Markers are provided to indicate the start and stop times of the media. In this way, any time εcale may be aεεociated with a media, and media start times may be set without requiring a separate calculation or application of offsets (since a clock's offset is only relative to its maεter clock) . At the physical level, all media player objects are slaved to the hardware portion of a RootClock which operates at the speed of the fasteεt media player in the system (e.g., 44.1 KHz CD-quality audio) , thereby facilitating the scheduling of future events at a particular point in time (e.g., corresponding to any individual media sample) . Since the speed of the RootClock iε equal to the faεtest media player in the system, time units for any other media player in the εystem can be "down-converted" from the rate of the RootClock. Moreover, the speed of the hardware portion of the RootClock is still relatively slow, slow enough to permit sufficient processing between hardware ticks. In another embodiment, separate RootClocks can be employed for the different speeds of each desired media player. The RootClock includeε a counter which maintainε a time value. Thiε counter may be entirely hardware, entirely software, or a combination of hardware and software. If a portion of the counter iε in hardware, interruptε to the εystem may be reduced. In this case, it may also be desirable to associate with the hardware portion of the RootClock a compare register of equal εize for the purpose of generating interrupts. Brief Description of the Drawinqε The preεent invention will be described in greater detail below, including specific examples thereof, with regard to the figures, in which: Fig. 1 is an illustration of the general computer architecture of a system within which the present invention may operate; Fig. 2 is an illustration of an exemplary claεε hierarchy of various claεεes according to one embodiment of the present invention; Fig. 3 is an illustration of rateε, εcales, and time values; Fig. 4 is an illustration of effective rates; Fig. 5 is an illustration of the subclasses of the CallBack class according to one embodiment of the present invention; Fig. 6 iε an illuεtration of a network of media players, hierarchically arranged, according to one embodiment of the present invention, for the "playing" of a multimedia title; Fig. 7 is an illustration of a synchronization εcheme for the playing of a multimedia title by the network of media playerε illuεtrated in Fig. 6; Fig. 8 iε an illuεtration of a variation of the εynchronization scheme for playing a multimedia title of Fig. 7; and Fig. 9 is also an illustration of a variation of the εynchronization εcheme for playing a multimedia title of Fig. 7. Aε between each of these figures, like reference numerals εhall denote like elements. Detailed Description For purposeε of illuεtration, the present invention will be described by way of εelected exampleε (or applications) , with reference to a number of embodiments of the present invention where appropriate. It will be apparent to one skilled in the art that the examples, and the environment in which they are developed, demonstrate the functionality and features of the present invention. It will also be apparent to one skilled in the art that certain variations, additionε, deletions, modifications, etc., to the examples are contemplated, and that recitation of these exampleε doeε not limit the scope of the invention. With regard to Fig. 1, there is shown therein the general architecture 10 of a system of the type within which the present invention operates. Architecture 10 comprises a main bus 12, which serves to interconnect various components, including at least some of the following (and posεibly other additional componentε) : Central Proceεεing Unit (CPU) 14, Floating Point Unit (FPU) 16, Buε Controller 20, Video RAM 22, Dynamic RAM (DRAM) 24, Static RAM (SRAM) 26, Digital Signal Proceεεor (DSP) 28, Internal Hard Diεk 30, External Memory Device 32 (connected for example via a SCSI port 34) , External Network Devices 36 (communicating for example over an Ethernet Network 38, and connected via SCSI port 34), Display Device 40 (such as a CRT) , Printer 42 (such as a PostScript device connected for example via a serial port 44) , Keyboard 46, and Pointing Device 48 (such as a mouεe, trackball, etc.) The interconnection and functioning of each of theεe components in an operating computer syεtem are well known in the art. However, the function and εignificance of particular componentε will be diεcuεsed in further detail where appropriate. While the discussion that follows describes the invention in terms of the εoftware programming environment known commonly as object oriented software design, it will be appreciated that the functionality of the present invention is not limited to εuch environments. However, as support for one possible environment in which the present invention operateε, a description of certain relevant details of object oriented programming environments is presented. In an object oriented programming language, the fundamental data εtructureε of the language are objectε, programming elements that contain a specification of both data and actionε. Data are specified in local variables, referred to as inεtance variableε, contained within the object. Actionε, or methodε, are subprograms that operate on the variables. Methods are invoked by mesεages sent from one object to itεelf or other objects. There are two fundamental object constructε: claεses and instances. Classes have a set of variables and methodε and can be thought of as templates for object typeε. Instances (or objects) are particular run-time instantiationε of a claεε. An object provideε storage for variables defined in itε class. Each instance has its own version of those variableε. When a meεεage iε εent to an object, the object looks to methodε defined in its class to determine how the message is to be executed. Classes are defined in terms of a clasε hierarchy. A claεε inheritε all variableε and methodε from claεεeε higher in the hierarchy, referred to as superclasεeε. The inheriting claεε may be referred to aε a εubclass or child of the superclass. The variables and methods inherited from a superclasε are available to the inheriting class as if they were defined within the inheriting class. Note that if a subclaεε haε multiple εuperclasses, all the variables and methods from each superclasε are inherited. This iε often referred to aε multiple inheritance. There are two types of variableε that may be defined within a class. The first are clasε variables, whose εtorage iε εhared by all inεtanceε of the defining class. Class variables are typically uεed for coordination between classeε and inεtances. The second are instance variables, which are variableε εpecific to each particular instance. That is, separate storage space is allocated for each instance variable of each instance. Methodε εpecify the action to be performed when a message is sent to an object. When the mesεage iε sent to an object, the mesεage name is matched against method names defined for that object. The method actually executed is the method with the εame name as the message that is defined lowest in that object's clasε hierarchy. Messages can have parameters. When a message is sent, all actual parameterε are fully evaluated before a method is located for that message. Methods have formal parameters, correεponding to the actual parameterε in the message, and temporary variables. Temporary variables may be created when a mesεage is executed, and are available only with the scope of that method while the method is executing. Programs perform by sending messages to objects which invoke a method in an object's class or class hierarchy. Often, methods send messages to other objects, invoking other methods. Typically, each method returnε a reεult to the sender. At the heart of many languages, and especially an object oriented language, is a program εegment for interpreting and evaluating meεεageε and keeping track of where to return when methods call other methods. Object oriented programming environments can be implemented with many programming languages. One common example of an object oriented environment is the C++ environment, described in further detail in Ellis, Margaret and Bjarne Stroustrup, THE ANNOTATED C++ REFERENCE MANUAL (Addison-Weεley 1990) and Coplien, Jameε 0., ADVANCED C++ PROGRAMMING STYLES AND IDIOMS (Addison-Wesley 1992) . With regard to Fig. 2, there is shown therein an illuεtration of the class hierarchy 764 of various clasεeε according to one embodiment of the preεent invention. Fig. 2 illuεtrates the inheritance relationship between the various classes of hierarchy 764. For example, Timebase class 750 is the base clasε from which Clock claεε 752 inherits, as shown by the line 751 connecting Timebase claεε 750 and Clock claεε 752. Player class 754 inherits from Clock clasε 752 aε illustrated by line 753. AudioPlayer class 756, VideoPlayer class 758, and ScriptSequencePlayer class 760 inherit from Player class 754, as illustrated by lines 755, 757, and 759, respectively. Initially, these clasεeε will be deεcribed, followed by an example of their uεage. Shown in Fig. 2 iε the relationεhip between the Timebaεe claεs 750 and a RootClock class 762. An instance of RootClock 762 (i.e., a RootClock object) can be comprised of both a hardware portion, and a software portion diεcuεεed in detail below. Each instance of the classes of hierarchy 764 must be synchronized directly or indirectly to a RootClock. Each object gets its time from an object which either directly or indirectly gets time from a RootClock. Hence, Timebaεe claεε 750 includeε a method for getting time from the RootClock. The hardware clock portion of a RootClock object may be, for example, a hardware device that emitε ticks at a specific rate together with a register which keeps track of those ticks, as discussed above. There is only a single RootClock object which represents that hardware device. That is, a RootClock represents a hardware timing resource. However, there may be within a single system multiple hardware timing resources, and thus multiple RootClocks, one for each hardware timing resource. As illustrated in Fig. 2, Timebase object 750 is the top-level class of hierarchy 764. When a Clock object, a Player object, an AudioPlayer, VideoPlayer, or ScriptSequencePlayer object is instantiated, it includes all methods and variables inherited from the Timebase clasε 750. This motivates the lexical statement that a Clock "is a" Timebase. The class methods for the Timebase class 750 are listed in Appendix 1. The instance methods for the Timebaεe claεε 750 are listed in Appendix 2. A Clock object (an instance of Clock clasε 752) iε principally capable of returning the time (hence the motivation for its name) . A Clock object records time by keeping track of the offset between itεelf and its master clock. When a Clock object receives a requeεt for the time, it gets the time of the master clock, subtracts the offset, and returns the result. Each Clock object has associated with it a time εcale that defineε the number of time unitε that pass each second (when rate is 1) . Therefore, a Clock object that haε a time scale of 1 measures time in secondε. Similarly, a Clock object that has a time scale of 60 eaεureε εixtiethε of a εecond. A particular point in time in a Clock object is represented by a time value. A time value is expressed in the time scale of the Clock object. For example, for a Clock with a time scale of 60, a time value of 180 translates into 3 seconds of elapsed time. The rate of a Clock object is the speed at which time passes for that object. Thus, the absolute value of a time unit in seconds depends on both the rate and scale of the Clock object. The number of time units that passes each second for a Clock object can be determined by multiplying its rate by its scale. The present time in seconds in the playing of a media may be determined as follows: time value Time in seconds = scale x rate Rates, time scales and time values are illustrated in Fig. 3. Inεtances of Clock class 752 may be created for the purpose of establishing a time source which does not play media. Instances of the AudioPlayer clasε 756, VideoPlayer class 758, and ScriptSequencePlayer class 760 may be created to obtain a time source which also plays specific media, as described below. A prototype for the method called on Clock class 752 to create a Clock object iε aε follows: method object new (class self object maεter object scale) The arguments of this method are: self The class to be instantiated, which in this case iε Clock. maεter The master clock to which the new clock is to be synchronized. If it iε paεsed as NULL, the clock is synchronized to a RootClock. scale The scale for the clock. An example of this method is: myclock = new(Clock, Null, 60) ; which creates a new Clock object synchronized to a default hardware clock, with a εcale of 60. The Clock claεε 752 inherits all of the methods and variables from the Timebase class 750. For example, the following methods inherited from the Timebase class 750 may be useful to Clock objects (see Table 2 for further descriptions of these methods) : getRate setRate getEffectiveRate getFlagε setFlags getMasterClock setMasterClock getMasterRootClock getRootClock ServicingCallBacks Timebaεe class 750 does not, however, provide time scales. The Clock class 752 provides methods for getting and setting time scales. Furthermore, Clock clasε 752 provideε methods for getting and setting its own time. Appendix 3 lists the methods that are introduced by the Clock claεs 752. The Player class 754 provides methods for playing media. Specifically, a Player object iε reεponεible for facilitating the data tranεfer between a media stream object (representing, for example, digitally captured audio or video) and a media system resource (e.g., driver for audio or video presentation devices that convert digital data to analog sound or images) . Such protocols include the information necessary to interpret the data stream. For example, an AudioPlayer object would be responεible for determining that an audio channel driver object (the methods for which are liεted in Appendix 8) iε capable of proceεεing the data at an appropriate rate - e.g., one corresponding to the sampling rate for a particular audio media stream. In this way, a Player object may assist in the identification and selection of an appropriate system resource for a particular data εtream. The Player class 754 defines a protocol which iε generic for all playerε. Thus, a Player object may also be employed as a high level controller of AudioPlayer, VideoPlayer, or ScriptSequencePlayer objects synchronized to that Player object. One key aspect of the present invention is that Player objects are also Clock objects (or in the parlance, a Player "is a" Clock) . Therefore, Player objects themselves contain methods involving time, such as methods for controlling the start and stop time, setting rate of play, etc. While the Player claεε 754 containε general methodε common to all players, each of the specific player subclasses, AudioPlayer class 756, VideoPlayer class 758, and ScriptSequencePlayer clasε 760, containε methods that are specific to its associated media. For example, AudioPlayer clasε 756 will contain methods for adjusting the play volume, etc., in addition to methods for controlling the start and stop time, εetting rate of play, etc. Appendix 5 presents a detailed discussion of a number of specific Player subclasses. Since εynchronization cauεes the time, rate, and offset of an object to be relative to another object (or to the hardware clock) , notice of a change in any of these values must be passed to all interested objects. That is, if a particular Player object is synchronized to a Clock object, its effective rate iε a function of the rate of the Clock object. For example, suppose a Clock object called ClockC, whose rate is 2, is synchronized to a Clock object called ClockB, whose rate is 6, which in turn is synchronized to a Clock object called ClockA, whose rate iε 3 aε εynchronized to the hardware clock. Aε illuεtrated in Fig. 4, ClockA'ε effective rate iε 3, ClockB'ε effective rate iε 18, and ClockC'ε effective rate is 36. Thus, if the rate of a Clock object changes, all objects synchronized to that object must be notified of the change. This notification is handled by CallBack objects. CallBack objects may also be uεed in conjunction with a Clock object to schedule the occurrence of activities at particular times. For example, a Player could be scheduled to start playing at a particular time. Thuε, to εchedule an activity, a CallBack object is created and associated with a Clock object. As illustrated in Fig..5, the CallBack clasε 780 haε the following εubclaεεeε: TimeCallBack class 782 These CallBacks are activated at a certain time. For example, a CallBack may be uεed to εtart a player at a particular time. RateCallBack class 784 These CallBacks are activated when the rate changes. For example, a CallBack may be used to alter the display when a media is in faεt forward mode. PeriodicCallBack class 786 These CallBackε are activated repeatedly at regular intervals. For example, during the playback of a movie, a CallBack could be used to diεplay the name of the producer every five εeconds for the first minute of playback. TickCallBack class 788 These CallBacks are εimilar to PeriodicCallBackε, but εuch a CallBack alwayε executes once per RootClock tick (or resolution) . TJumpCallBack class 790 These CallBacks are activated when there is a jump in time. For example, during the playing of an animation εequence, if the time is reset, a CallBack could be uεed to do certain houεekeeping functionε to reset the animation. CallBack objects are created by first ensuring that the clock which it will be attached to exists. Next, a new CallBack object is created by calling the new method on the appropriate CallBack subclass. In creating the new CallBack object, the clock which it will be attached to is specified. A function is then εpecified, with a single argument of type void * , for the CallBack to perform. The callMeWhen method of the CallBack object is used to specify when the CallBack is to be activated. The prototype for callMeWhen is: method void callMeWhen( object self, CallBackProc CallBackProc, void "CallBackParam, long flags, long rateORline, TimeRecord 'timerecord, CallBackPriority queuelD) The argumentε of callMeWhen are: self The CallBack CallBackProc The procedure that defines what the CallBack doeε CallBackParam The argument of type Void for CallBackProc. flags This flag can be one of the following, which have all been defined as type long: triggerTimeFwd The CallBack will be triggered at a given time when the rate is positive (that iε, going forward.) This only applies to TimeCallBacks. triggerTimeBwd The CallBack will be triggered at a given time when the rate is negative (that iε, going backward.) This only applieε to TimeCallBack . triggerTimeEither The CallBack will be triggered at a given time when the rate iε either positive or negative. This only applies to TimeCallBacks. triggerRateLT The CallBack will be triggered when the rate is lesε than a given value. This only applies to RateCallBacks. triggerRateGT The CallBack will be triggered when the rate is greater than a given value. This only applies to RateCallBacks. triggerRateEqual The CallBack will be triggered when the rate is equal to a given value. Thiε only applies to RateCallBacks. triggerRateLTE The CallBack will be triggered when the rate iε less than or equal to a given value. This only applies to RateCallBacks. triggerRateGTE The CallBack will be triggered when the rate is greater than or equal to a given value. This only applies to RateCallBacks. triggerRateNotEqual The CallBack will be triggered when the rate iε not equal to a given value. This only applies to RateCallBacks. triggerRateChange The CallBack will be triggered when the rate changes. This only applieε to RateCallBackε. none/0/null For TJumpCallBackε, TickCallBackε and PeriodicCallBackε. rateORline Thiε applies to RateCallBacks only. For other types of CallBacks, pass this as NULL. The specified rate is the critical rate that determines when the CallBack iε invoked. For example, if the flag is triggerRateGTE, and the rateORline is 10, the CallBack will be triggered any time the rate iε 10 or greater. The line value iε uεed for diεplay- baεed clocks where you might be able to interrupt on a particular scan- line. timerecord Thiε applies only to TimeCallBacks and PeriodicCallBacks. For other types of CallBackε, paεε thiε aε NULL. The time value iε a 64-bit integer, which must be addressed as two longs (in most programming languageε) . Thiε iε the time record that indicateε the time at which the CallBack iε to be activated for TimeCallBacks, and the time period between activations for PeriodicCallBacks. CallBack This can be one of the following: Priority lowCallBackPriority medCallBackPriority highCallBackPriority The priority value is used to help reεolve conflicts when multiple CallBacks are scheduled to go off at the same time, (but there is no absolute guarantee about what order they will go off in.) The priority also affects the responsiveness of the CallBack: the higher the priority, the closer to the right time that the CallBack will be executed. For example, suppoεe a uεer deεires to create a CallBack to start a given player playing at time 10. The following example shows the code for the CallBack procedure StartPlay, which starts a player playing. It then shows a function SetCallBackToGo that setε the time and procedure for the CallBack, then attacheε the CallBack to a given player. void StartPlay (void Value) { object player = (object) value; play (player) ; } void SetCallBackToGo(object player, long startTime) ; { object callback = new(TimeCallBack, player) ; TimeRecord timerecord; timerecord.value.high = 0; timerecord.value.low = startTime; timerecord.scale = 1 callMeWhen ( callback, StartPlay, player, triggerTimeFwd, 0 , Sttimerecord , highCallBackPriority) ; } The CallBack claεε iε an abεtract class, so the user does not typically create instances of it. Instead, a user would create an instance of the appropriate subclass (TimeCallBack, RateCallBack, PeriodicCallBack, TickCallBack, and TJumpCallBack) . Each of these subclasεes has a "new" method with the following prototype: method object new (object self, object clock) where the arguments are: self is one of TimeCallBack, PeriodicCallBack, RateCallBack, TJumpCallBack and TickCallBack depending on what type of CallBack you want. clock is the clock to which to attach the CallBack. Finally, Appendix 6 lists the instance methods of the CallBack subclasses. With regard now to Fig. 6, there is shown therein a network 800 of media player objects, hierarchically arranged, according to one embodiment of the present invention, for the "playing" of a multimedia title. The hierarchy indicates the master-εlave relationεhip between theεe player objectε. The network 800 of Fig. 6 will be used in the following example to illustrate various aspects and features of the present invention. Initially, each of the players must be created. This εtep may be performed by invoking the "new" method on each of the εubclasses ScriptSequencePlayer, AudioPlayer, and VideoPlayer. The "new" method for each of these particular subclaεεeε iε deεcribed in detail in Appendix 5. Each of the player objects must be asεociated with an exiεting data stream object, the playing of which is controlled by the player object. (Appendix 7 containε a list of methods for an Audio Stream object, as an example of methods for such data stream objectε.) Creation and εtorage of digitized streams of audio, video and other media data is well known in the art. The data stream objects are associated with the player objects by way of the arguments of the "new" method. Specifically, thiε results in the creation of ScriptSequencePlayer object 802, VideoPlayer object 804, and AudioPlayer object 806, within the context of computer 808. Theεe objectε must next be associated with one another, for example to establish the relative timing among them, for the purpose of playing the title. Fig. 7 illustrateε a synchronization scheme by which network 800 may play a title. The ScriptSequencePlayer 802 begins playing animation. Its master clock is the RootClock. The VideoPlayer 804 has its master clock set to the ScriptSequencePlayer 802. This may be accomplished by the setMasterClock method (Appendix 2) . After 5 units of the ScriptSequencePlayer's time have paεεed, the VideoPlayer 804 begins playing a video data stream at its own time 0. This is established by the setScaledClockZero method (Appendix 2) . Thus, the VideoPlayer 804 has an "offset" of 5. That iε, its "0" time is 5 units after the "0" time of its master clock (in the master clock's units) . Furthermore, the VideoPlayer'ε origin iε at 0. That iε, the VideoPlayer begins playing at its own time 0. The AudioPlayer 806 also has its master clock εet to the ScriptSequencePlayer 802. After 10 units of the ScriptSequencePlayer's time haε passed, the AudioPlayer 806 begins playing an audio data stream. However, the start of the AudioPlayer'ε time corresponds to the start of the ScriptSequencePlayer's time. Thus, the AudioPlayer has an offset of 0, with its origin at 10 (by invoking the setOrigin method) . Importantly, it iε the fact that each player inheritε the Clock class methods (i.e., a player "is a" clock) which allow a player to have its master clock set to another player — it is not neceεεary to separately addresε clock objects. A player hierarchy has thereby been eεtabliεhed, with the playerε aεεociated with data stream objects and with the various players εynchronized. The play method may then be invoked on the ScriptSequencePlayer. This results in setting the rate of the ScriptSequencePlayer to 1.0 (wherein a rate of 1.0 corresponds to "play," a rate of 0.0 correspondε to "εtop," a rate of -1.0 corresponds to play in reverse, a rate of 0.5 corresponds to play at half speed, etc.). Each Player object, by way of methods inherited from the Timebase clasε, maintains a list of CallBacks which contain objects to be called and the event upon which they are to be called. A player which is "intereεted" in (e.g., affected by) a time or rate change, overrides the timeChanged or rateChanged methods of the superclaεε. When the setTime or setRate methodε are called, any CallBacks asεociated with a time change or rate change are dispatched, respectively. In addition, a Player issues a timeChanged or rateChanged message directly to itself and all playerε εynchronized to it. Within the timeChanged or rateChanaged method, if it iε determined that the player iε approaching a time at which it is to play, it registers a TimeCallBack with itself. This TimeCallBack will dispatch a play message at the appropriate time. If it is determined by the player that it iε at a time at which it should play / no CallBack is registered, and play is invoked immediately. Due to the rate being changed on ScriptSequencePlayer 802, a rateChanged method is called on each of the slaved players, VideoPlayer 804 and AudioPlayer 806. This results in CallBacks being scheduled, as discuεsed above. The first TimeCallBack is set for VideoPlayer 804 at time 5 of ScriptSequencePlayer 802, and the second iε εet for AudioPlayer 806 at time 10 of ScriptSequencePlayer 802. Upon determining that time 5 has been reached, the RootClock sendε a play meεεage to VideoPlayer 804 via the CallBack. Likewiεe, the play method of AudioPlayer 806 iε invoked upon reaching time 10. It will be appreciated that εetting the time for the CallBack iε a function of the application environment in which the preεent invention is operating. That is, in the above example it may be desirable or required to set a CallBack to occur before the media is actually to play, for the purpose of preparing the player, hardware, etc. As a first variation on the above example, suppose it is desirable to silence the AudioPlayer 806 for a portion of its play time, but keep its time running for later play (as opposed to a pause in the playback) . Thiε may be accompliεhed by turning AudioPlayer 806 off and then on again, but thiε would require the additional εteps of maintaining the duration of the off-time, calculating the on-time, and setting the time to that on-time. A εimpler mechanism for accomplishing this, and one more in keeping with the hardware player analog, is to provide a mute feature. The mute feature may be scheduled via a CallBack. Thiε mute feature allowε a player to continue to count time, while εilencing its output. Fig. 7 shows AudioPlayer 806 muted from its time 13 to its time 16. As a second variation on the above example, asεume that it is desired to go to a particular time on the script εequence of network 800 and begin playing. This is accomplished by the εetTime method of the ScriptSequencePlayer 802 (Appendix 3) . Specifically, εuppose that in the play of the script sequence, an event occurs which causes the lay of the script sequence to return to its time 5 (for example, a user pushes a button that caused this command to be sent to the script sequence) . The result is that the VideoPlayer 804 and AudioPlayer 806 receive a timeChanged mesεage from the ScriptSequencePlayer 902 indicating that time haε been changed, and the playerε accommodate the meεεage aε discusεed above (e.g., VideoPlayer 804 starts at its time 0, and AudioPlayer 806 εtartε at itε time 5) . It will be appreciated that again it iε the inheritance hierarchy (i.e., a player "iε a" clock) which facilitates this simple compensation for time changeε. Aε another variation of the above-deεcribed example, εuppoεe it is desirable to go to a particular time of the video playback, independently of the ScriptSequencePlayer. That is, it is desired to alter the εynchronization between the video and εcript playback. Thiε may be accomplished by invoking the setTime method of VideoPlayer 804. Specifically, suppose that when time 12 in the ScriptSequencePlayer's time iε reached, VideoPlayer 804 receiveε a call to set its own time to 10, eεεentially εkipping forward. Thiε is shown graphically in Fig. 8. The result of this call is to change the offset of VideoPlayer 804 relative to ScriptSequencePlayer 802 from 5 to 2. It εhould be noted that the change only affects VideoPlayer 804; ScriptSequencePlayer 802 and AudioPlayer 806 are unaffected by the change. As yet another variation on the above example, suppose that it is desired to change the start time of the animation played by the ScriptSequencePlayer 802, yet leave the synchronization relationships between the players unchanged. For example, suppoεe that it iε desired that the script sequence start playing at itε own time 5, coincident with the start of VideoPlayer 804, while the point in time at which its clock starts remains unchanged. This may be accomplished by invoking the setOrigin function for ScriptSequencePlayer 802 to set the origin to 5. Notice that changing origin has no effect on offset, as shown in Fig. 9. Aε εtill another variation of the example diεcuεsed above, assume that it is desirable to play the script sequence at an accelerated rate, for example to double itε rate of play. Thiε may be accomplished by invoking the setRate method (Appendix 2) on ScriptSequencePlayer 802. The net effect of this method is to double the rate of play of ScriptSequencePlayer 802. Importantly, the result of doubling the rate of ScriptSequencePlayer 802 is also to double the rates of play of the clockε (and thus) players slaved to it, namely VideoPlayer 804 and AudioPlayer 806. This simple method for coordinating modifications to a master clock is, once again, facilitated by the inheritance of clock methods by a player object (i.e., a player "is a" clock). As previously mentioned, CallBack objects associated with Timebase objectε are registered with the RootClock of the Timebase object. These CallBack objects are maintained in a time-ordered list in the RootClock. CallBack objects can be registered according to (i.e., an object may request notification of setting or changes to) time or rate. CallBacks which return a message at a particular time must be εcheduled differently. The time of the CallBack iε εpecified in the εcale of the associated Clock. This time is converted to the scale of the RootClock, added to the current tick count of the counter, and inserted in the timeordered list in the RootClock. The manner in which the RootClock object determines when to dispatch a CallBack will now be discussed. With regard to the hardware portion of the RootClock 762 to which timebaseε muεt ultimately be εynchronized, most computer syεtems rely on the only readily available and feasible constant hardware tick - the vertical synchronization signal (VBL) , which typically oscillates at 60 Hertz. A software counter is generally employed to maintain a count of ticks, e.g., in a 64-bit integer. In this manner, the system is interrupted every 1/60 second, whereupon the software counter is incremented. Yet, in multimedia applications, the reεolution of 1/60 εecond iε not εufficient. For example, the standard sound εampling rate is 44.1 KHz. Thus, there are 735 samples between each tick. Accessing a precise one of the 735 samples is impossible with a 60 Hz clock. However, few (if any) computer platforms are capable of sustaining interrupts at a rate of 44.1 KHz. The conεequence iε that exiεting εyεtems either accept this lack of precise synchronization or attempt to use a faεter clock (e.g., a 25 MHz system clock to which their software clocks are not synchronized) to estimate the deεired time. In either case, the result is less than accurate synchronization. According to one embodiment of the present invention, the playerε (and thuε clockε) in the network hierarchy of Fig. 6 are ultimately εynchronized to a root clock which operates at 44.1 KHz (the rate of the fastest media in the system - CD-quality audio - which can be converted to the slower rates of other media, such aε the 30 frames/second of full motion video) . In this manner, precise synchronization to any εample of CD-quality audio or virtually any other media can be obtained. To avoid overloading the εyεtem with frequent interruptε aε noted above, the RootClock object to which ScriptSequencePlayer 802 is synchronized is provided with a 16-bit hardware counter portion which generates an interrupt when it wrapε around (overflowε) , approximately once every 1.5 seconds, and a 48-bit software counter portion. The interrupt εignal from the RootClock's 16-bit hardware counter portion is uεed to increment its 48-bit software counter portion. Thuε, together theεe hardware and εoftware portions of the RootClock form a 64-bit hardware/software root clock operating at 44.1 KHz. In addition, the RootClock is provided with one or more 16-bit compare registers used for low order bit comparisons of CallBacks. For each increment of the εoftware counter, the first CallBack in the time-ordered list is checked. To determine if a CallBack should be εcheduled the current value of the 64-bit RootClock counter iε εubtracted from the 64-bit CallBack value. If the result of the subtraction is less than the bit- resolution of the hardware counter (i.e., 65,536 for 16 bits) then the low-order 16 bits of the CallBack's value are placed in the hardware compare regiεter (unless the result iε less than or equal to zero, in which case the CallBack is immediately dispatched) . If the reεult of the εubtraction iε greater than the bit reεolution of the hardware counter, then the hardware counter iε allowed to roll-over, and the subtraction is performed again. When the low-order 16 bits of the CallBack's value are latched into the hardware compare register, the CallBack interrupt is enabled. When the 16-bit hardware counter equals the value in the compare register, the CallBack interrupt is generated. The RootClock disableε the interrupt and dispatcheε the CallBack (as discussed above) . As well understood by those skilled in the art, this dispatch may come in the form of enabling a task to handle the CallBack, εince interrupt routines εhould be minimized where poεεible. In general, to those skilled in the art to which thiε invention relates, many changes in construction and widely differing embodiments and applications of the preεent invention will εuggeεt themselves without departing from its spirit and scope. For example, players other than thoεe diεcuεεed above may be employed in hierarchieε of the type illustrated herein. Thus, the disclosures and descriptions herein are illustrative, and are not intended and should not be read to be in any sense limiting. Appendix 1 The methods for the Timebase class generally take arguments of type TimeValue, TimeScale, and TimeRecord. Definitions for these data types are as follows: typedef long TimeValue; typedef unsigned long TimeScale; typedef KDoubleLong CompTimeValue; typedef struct TimeRecord { CompTimeValue value; /*units*/ TimeScale scale; /*units per second*/ object timebase; /*usually TimeBase*/ } TimeRecord; Timebase Class Methods Argument Name Type Type Argument Description new object class self Creates a new instance of the class, initializing all the instance variables. convertTimeScale void class self Converts a time TimeRecord *timerec from one time timeScale scale to scale another. Specify the time to be converted in a time record. Argument Name Type τ y e Argument Description addTime void class self Adds two times together. TimeRecord *dst Specify the times in time TimeRecord *src records. If these times are relative to different time scales or clocks, the addTime method converts the times as appropriate to yield reasonable results. However, the clocks for both time values must rely on the same time source. subtractTime void class self Subtracts one time from TimeRecord *dst another. Specify the TimeRecord *src times in time records. If these times are relative to different time scales or clocks, the subtractTime method converts the times as appropriate to yield reasonable results. However, the clocks for both time values must rely on the same time source. Appendix 2 Timebase Instance Methods Argument Name Type Type Argument Description convertScaledTime void object self Converts a time into a TimeRecord timerec time that is relative to this clock. Specify the time to be converted in time record. getScaledTime TimeValue object self Returns the clock's TimeScale scale current time in the scale TimeRecord *timerec specified by the scale. Timerec is either a pointer to a TimeRecord, or NULL. If no TimeRecord is specified, then the time is returned as a TimeValue (which is a long) . If the time value is greater than can be specified in a long, the returned value is set to the largest value that a long can hold. If a TimeRecord is specified, then additionally the time field is filled in with the clock's time value as a KDoubleLong Argument Name Type Type Argument Description setScaledTime void object self Sets the current time TimeRecord "t of a clock to the time specified in the record and in the scale specified in the time record. If the current time of a clock that is the master clock for other clocks is set, the current times in all the slave clocks are changed appropriately. If the current time in a clock that relies on a master clock is changed, it changes the offset between the clock and the master clock— he master clock is not affected. Argument Name Type Type Argument Description setScaledValue void object self Sets the current time TimeValue time of a clock in the given time TimeScale scale scale. Specify the new time as a time value. If the current time of a clock that is the master clock for other clocks is set, the current times in all the slave clocks are changed appropriately. If the current time in a clock that relies on a master clock is changed, it changes the offset between the clock and the master clock—the master clock is not affected. getRate KFixed object self Returns the rate of a clock. setRate void object self Sets a clock's playback rate. KFixed rate Rates may be set to negative values. Negative rates cause time to run backwards. getEffectiveRate KFixed object self Retrieves the effective rate of a clock by taking into account the rates of all the clocks to which it is slaved. Argument Name τy £ Type Argument Description If it is not slaved to any other clocks, it returns the same result as getRate returns. getFlags long object self Allows an application to obtain the contents of the control flags of a clock. The flags are listed in the description for setFlags below. Argument Name Type Type Argument Description setFlags void object self Sets the contents of long flag the looping control flags of a clock. The choices for flag are: (defined as longs) 1 oopT±meBase Indicates whether the clock loops. If this flag is set to 1 and the rate is positive, the clock loops back and restarts from its start time when it reaches its stop time. If this flag is set to 1 and the rate is negative, the clock loops to its stop time. If the flag is set to 0 the clock stops when it reaches the end. palindromeLoop -TlmeBase Indicates whether the clock loops. If this flag is set to 1, the clock loops back and forth between its start time and its stop time, Argument Name Type Type Argument Description regardless of the rate setting. If the flag is set to 0 the clock stops when it reaches the end. getMasterClock object object self Returns the clock to which this clock is directly synced. Returns NULL pointer if it is directly synchronized to a hardware clock. setMasterClock void object self Synchronizes the clock to object clockTo- another clock. SyncTo getMasterRoot- object object self Returns the Clock hardware clock to which this clock (self) is directly synchronized. Will return NULL pointer if it is not directly synchronized to a hardware clock. Argument Name Type Type Argument Description getRoo Clock object object self Gets the root hardware clock of a clock object, regardless of what its master clock is. For example, if ClockA is synchronized to ClockB which is synchronized to a hardware clock, ClockC, then a call to getRootClock on ClockA will return the hardware clock ClockC. setScaledClock- void object self Changes the Zero offset from a TimeRecord *zero clock to its master clock. The initial offset is established when a clock is assigned to its time source (use the setMasterClock procedure to assign a clock to a master clock) . Argument Name τ 7P e τ 7P e Argument Description getScaledStatus long object self Retrieves status TimeRecord *timerec information from a clock. Returns flags that indicate whether the returned time value is outside the range of values specified by the start and stop times of the clock. This can happen when a clock relies on a master clock or when its time has reached the stop time. The following flags are defined: timeBaseBefore -StartTime Indicates that the time value represented by the contents of the time record referred to by the unpinnedTime parameter lies before the start time of the clock. This flag is set to 1 if the current time is before the start time of the clock. append void object self Adds a CallBack object CallBack object to the list for this clock. Argument Name τyp 6 τyp e Argument Description deleteone void object self Removes a CallBack object CallBack object from the list for this clock. ServicingCall- KBoolean object self Returns true backs if the CallBacks associated with this clock are being rescheduled. getMasterScale long object self Returns the scale of the master clock. Appendix 3 Clock Instance Methods Argument Name Type Type Argument Description getScale TimeScale object clock Gets the scale of the clock. setScale void object clock Sets the scale of TimeScale scale the clock. getTime TimeValue object clock Writes the name of TimeValue *time the clock, in the clock's own time scale, into the timevalue. setTime void object clock Sets the time of the TimeValue *time clock in the clock's own time scale. Appendix 4 Player Instance Methods Argument Name Type Type Argument Description play void Player self Starts playing. record void Player self Records if recording is possible. stop void Player self Stops playing. mediaEject void Player self Ejects if ejection is possible. pause void Player self Sets the rate of the player to zero, but it is still prepared to continue. getMuted long Player self Returns true (1) if the player has been muted, otherwise returns false (0) . setMuted long Player self If MUTED is 1, long muted sets the player to be muted. playPrepare void Player self Prepares the player for the immediate playback. This means that hardware resources are allocated to this player. playUnPrepare void Player self Releases the hardware and software resources used by the player. goToBegin void Player self Resets the time to 0. goToEnd void Player self Returns the time to duration (as returned by getDuration) . getDuration Time- Player self Returns the Value TimeRecord *timeRec current duration. goToMarker void object self Goes to the marker TimeRecord index at the specified index. Argument Name Type Type Argument Description setOrigin void Player self Sets the origin value of a player. getOrigin long Player self Retrieves the origin value of a player. Playing Digitized Audio To play a digitized sound, create an audio stream for the sound. Then create a DigitizedAudioPlayer, and specify the input stream. Then call the play method on the player. For example, suppose that a Bento file contains the digitized sound of a whale spouting. This sound is identified as value 65574. The following function will play the sound of a spouting whale: void MyPlayFn ( ) ( object mystream = new(AIFFStream, new(long 65574)) ; object myplayer = new(DigitalAudioPlayer, mystream) ; play(myplayer) : The CDAudioPlayer Class NYI - Not yet implemented. Use instances of the CDAudioPlayer class to play sound on CDs. Instance Methods on Classes for Playing Audio This section lists the instance methods on AudioPlayer, followed by the additional instance methods on DigitalAudioPlayer, followed by the additional methods on CDAudioPlayer. Instance Methods on AudioPlayer AudioPlayer inherits methods that are generic to all players from Player and methods that are generic to all clocks from Clock. The methods inherited from Player, which are play record stop mediaEject pause getMuted setMuted playPrepare unPrepare goToBegin goToEnd getDuration The methods inherited from Clock that are relevant to Player objects, getScale setScale getTime setTime getRate setRate getEffeetive-Rate getFlags setFlags getMasterClock setMasterClock getRootClock getMasterRootClock servicingCallbacks The additional methods in AudioPlayer that are specific to playing audio are listed below. Argument Name Type Type/Class Argument Description setGain void AudioPlayer self Sets the gain (volume) of the player. The long gain gain value is between 0 and 2 16 -1 where 0 means no sound and 2 16 - 1 means the loudest that can be played. getGain long AudioPlayer self Gets the gain (volume) value of the player. setPan void AudioPlayer self Sets the pan (balance) for the sound that the long pan player controls. The value is between 0 and 2 16 - 1.0 means the sound is all the way to the left, and the maximum value means it is all the way to the right. (You can use the constant kUnityGain for the midway point at which the sound is equally balanced between left and right. getPan long AudioPlayer self Gets the value of the pan (balance. Instance Methods on DigitalAudioPlayer The DigitalAudioPlayer class inherits methods that are generic to clocks from Clock methods that are generic to all players from Player and methods that are generic to playing sound from AudioPlayer. The additional methods in DigitalAudioPlayer that are specific to playing digital audio are listed below. Argument Name Type Type/Class Argument Description getSampleRate KUFixed AudioPlayer self Gets the sample rate of the input stream. setPitch void AudioPlayer self Sets the pitch NYI - not yet for the sound implemented short pitch that the player controls. Pitch is specified as MIDI note number. get Pitch short AudioPlayer self Gets the pitch NYI - not yet of the sound implemented that the player controls. getCurrentSample KDouble- AudioPlayer self Returns a Long number that is the count of the current sample, offset from the beginning of the file. getlnputStream object AudioPlayer self Returns the AudioStream that the player plays. getlnputStream void AudioPlayer self Sets the AudioStream stream AudioStream that the player plays. Instance Methods on CDAudioPlayer The CDAudioPlayer class inherits methods that are generic to clocks from Clock methods that are generic to all players from Player and methods that are generic to playing sound from AudioPlayer. The additional methods in CDAudioPlayer that are specific to playing digital audio are listed below. Argument Name Type Type/Class Argument Description setTrack void CDAudioPlayer self Sets the track. long track getTrack long CDAudioPlayer self Gets the current track. nextTrack void CDAudioPlayer self Sets the track value to the next track (after the current track value. ) previousTrack void CDAudioPlayer self Sets the track value to the previous track (after the current track value.) Playing Movies The MoviePlayer class has methods for controlling the playing of movies. It inherits generic Player methods, such as play, stop and so on from the class Player. Additionally it has methods that are specific for controlling the playing of movies. A MoviePlayer object has an associated Stream object that represents the movie to be played. The Stream contains the data for the movie. It is used to access all the movie's sample data, as well as all the control information for tracks and media (this is true for sound too. )' Any type of stream can be used as the source for the movie's data, providing device and filesystem independence. The only requirements are that the stream supports seeking to an absolute location and reading a block. Obviously, very slow streams will not produce optimum results with this player. Also, note that if a Bento stream is used, or if some other wrapper is placed around the movie data, then the location of the various data chunks relative to the beginning of the stream must be preserved for the player to be able to map the data correctly. In other words, the mapping information that was written to the file when it was recorded must remain valid when it is played back. Specifying the Display Area for a Movie Your application can specify what display device the movie is to be played on, and on what part of the device the movie should appear. To specify the display device, call the MoviePlayer object's setGraphicsWorld method. By default on Sweet Pea, the graphics device is the CRT screen. To specify where on the display device the movie appears, set the bounds rectangle for the movie. You can do this by calling the MoviePlayer object's setMovieBounds method. Be default on Sweetpea, the movie appears in a rectangle in the middle of the CRT screen. The bounds rectangle is determined by a Rect structure that specifies the top, left, right, and bottom values of the rectangle. You can think of the bounds rectangle as being a movie screen. When a movie is created, it has a default screen size associated with it. In general, you should not change the screen size, since the movie image will lose quality if it is resized to fit a different size screen. 1 Macintosh-based QuickTime movies will need to be converted into a compatible format for use with the player. The current strategy for file conversion involves using a single-fork, self-contained movie file (as created by the Macintosh Movie Toolbox function FlattenMovie). However, you can change where on the display device the movie appears. To do this, you need to change the top left corner of the bounds rectangle without changing its width and height. To move the top left corner of a Rect structure, use the KOffsetRect function. To find the current bounds rectangle of a movie, call the MoviePlayer's getMovieBoundε method. For example, the following function moves the movie screen by x pixels to the right and y pixels down from its original location: void OffsetMovieBounds (moviePlayer, x, y) ( KRect boundsRect; getMovieBounds (moviePlayer, boundsRect); offsetRect (boundsRect, x, y); setMovieBounds (moviePlayer, boundsRect); ) Clipping Region In addition to specifying the size and location of the screen, you can specify a clipping region for the movie. The movie will only appear inside the clipping region. By default on Sweet Pea, the clipping region is set to the default bounds rectangle. The clipping region does not have to be a rectangular region. To specify a clipping region, call the setClipRgn method on the MoviePlayer object, and specify the region as a KRgnHandle. (See the Imaging Chapter for a discussion of how to create regions.) Any part of the movie image that falls outside the clipping region will be clipped, so make sure that the clipping region and the movie's bounds rectangle overlap. Movie Posters MoviePlayer objects can display a single frame of a movie as a poster. Use the setPosterTime method on the Movie¬ Player object to specify which time frame of the movie to use as the poster, and use the showPoster method to display the movie. The poster uses the same display device, bounds rectangle and clipping region as the movie. Controlling Sound for Movies The MoviePlayer class has methods for controlling the sound volume of movies and tracks. Track volumes allow tracks within the movie to have different volumes. A track's volume is scaled by the movie's volume to produce the track's final volume. Volume ranges from -1 to +1. Higher values indicate louder volumes. A value of 1 is equivalent to the loudest volume that can be played on the player. Negative values indicate muted volume. This is, the MoviePlayer does not pay any sound for movies or tracks with negative volume settings. However, the original volume level is retained as the absolute value of the volume setting. Tracks A movie can consist of several tracks. It usually has one track for audio and one for video, and may have additional tracks. The MoviePlayer class has several methods that provide individual control of tracks, such as the setTrackVolume method that sets the volume for a specific track. When using these methods, refer to specific tracks by their track number, which is a number between one and the number of tracks in the movie, inclusive. A Quicktime movie can contain alternate tracks that can be used to support multiple language or to present different levels of visual quality in a movie. Alternate tracks are arranged in groups when the movie is made. The MoviePlayer selects one track from each group when it plays the movie. For example, a movie might have three separate audio tracks; one in English, one in French, and one in Spanish. These tracks would be arranged in a group. When the user plays the movie, the MoviePlayer selects the track from the group that corresponds to the current language setting for the movie. Individual tracks can be enabled and disabled. For example, a movie could have two audio tracks, one for music and one for voice over. If you don't want to hear the voice over, you could disable the voice over track. Preferred Movie Settings Every movie has default, or preferred, settings for playback rate and volume. These settings are stored with the movie when it is created. The MoviePlayer object has methods for accessing these default settings, such as the getPreferredVolume method. How to Play a Movie To play a movie, create a Stream object for the movie data. Create a MoviePlayer object and specify the input stream. To play a movie, call the play method on the MoviePlayer object. So long as the movie has not been disabled, it will play. The movie appears in the previously-specified bounds rectangle on the previously-specified display device. Any part of the movie image that falls outside the clipping region will not appear. On Sweetpea, the display device default to the CRT screen, and the bounds rectangle defaults to a rectangular region in the middle of the screen. The clipping region defaults to the bounds rectangle, so no clipping occurs. When the play method on a MoviePlayer is called, the player plays the part of the movie specified by its play range, which defaults to the whole movie. You can use the setPlayRange method to specify the play range for the movie. This method takes arguments of the start time and the duration for the play range. One example of the use of play ranges is to specify a play range that corresponds to a preview of the movie. For example, you could play the first five seconds of the movie as a preview. Creating a New MoviePlayer To create a new MoviePlayer, call the new method on the MoviePlayer class. The protocol for this is: method object new (object self, object stream) The argumentε are: self The class to be instantiated, which in this case is MoviePlayer. inputStream The Stream object that represents the movie data. You can pass this as NULL to specify no input stream. This method creates a new instance of the MoviePlayer object. By default the new player is synchronized to a hardware clock. You can specify an input stream when you create a MoviePlayer or you can create the player without an input stream and then specify the input stream later by using the method setInputStream. Code Example Here's an example of the creation and use of a MoviePlayer object. This function takes a Stream that points to movie data. This example supposes that the frame at time 1 should be used as a poster, that the movie stream contains a preview between time 2 and 10, and the actual movie runs from time 12 to 112. This function shows the poster for five times units, shows the preview, waits for five times units, then shows the movie. void TestMoviePlayer (object movieStream) ( long i, tracks; usesClass (MoviePlayer); /* Create a movie player object */ moviePlayer = new (MoviePlayer, movieStream) ; /* Set the play range from time 12 for 100 time units */ setPlayRange (moviePlayer, 12, 100); play (MoviePlayer); ) Instance Methods in MoviePlayer MoviePlayer inherits methods that are generic to all players from Player and methods that are generic to all clocks from Clock. The method inherited from Player are discussed on page 4- 19. They are: play record stop mediaEject pause getMuted setMuted playPrepare unPrepare goToBegin goToEnd getDuration The methods inherited from Clock that are relevant to Player objects are given below. They are discussed on page 4-19. They are: getScale setScale getTime setTime getRate setRate getEffective-Ra e getFlags setFlags getMasterClock setMasterClock getRootClock getMasterRoot-Clock servicingCallbacks The additional methods on MoviePlayer that are specific to playing movies are listed below: Argument Name Type Type/Class Argument Description setActive void object self Sets the movie KBoolean active player to be active or not. getActive KBoolean object self Returns true if the movie player is active. isDone KBoolean object self Returns 1 if the movie has completely finished playing, else returns 0. A movie with a positive rate (it's playing forward) is considered done when its movie time reaches the end movie time. Conversely, a movie with a negative rate (it's playing backward) is considered done when its movie time reaches the movie start time. setPlayRange void object self Defines a movie's COSTimeValue startTime active segment. COSTimeValue duration Specify the starting time and duration of the active segment, which must be given in the movie's time scale. getPlayRange void object self Determines what COSTimeValue *startTime portion of the COSTimeValue *duration movie is currently active for playing. This will be the range set by setPlayRange if it has been called. The default is the entire movie if setPlayRange has not been called. showPoster void object self Displays a movie's poster. The movie player draws the movie poster once, in the same area in which the movie appears. setPosterTime void object self Sets the poster COSTimeValue posterTime time for the movie. Since the movie poster is a still frame, it is defined by a point in time within the movie. The poster time is in the movie player's time scale. getPosterTime COSTime- object self Returns the Value poster's time in the movie. Since the movie poster has no duration, a poster is defined by a point in time within the movie. The time value returned is in the movie player's time scale. Time Control Several of these methods take a track argument, which is the number of the track. The first track is 1.0, the second track is 2 and so on. Argument Name Type Type/Class Argument Description getPreferredRate KFixed object self Returns the default playback rate of the movie. This is the rate the play method uses when it starts playing the movie. The movie player multiplies its normal playback rate by the playback rate value to obtain the playback rate for your movie. For example, if a movie'ε playback rate value is 2, the movie player plays the movie at twice normal speed. The rate is returned as a 32-bit, fixed-point number. The high order 16 bits contain the integer part and the low-order 16 bits contain the fractional part. Positive integers indicate forward rates and negative integers indicate reverse rates. getTrackDuration COSTime- object self Returns the Value long track duration of a track. The duration corresponds to the ending time of the track in the movie player's time scale. setTrackOffset void object self Sets the time long track difference COSTimeValue offset between the start of a track and the start of the movie. This method modifies the duration of the empty space that lies at the beginning of the track, thus changing the duration of the entire track. Specify this time offset as a time value in the movie player's time scale. getTrackOffset COSTime¬ object self Returns the Value long track time difference between the start of a track and the start of the movie that contains the track. Graphics SetGraphicsWorld void object self Sets the object graphic- graphic Device device where the movie will play. On SweetPea, the default graphic device is the crt screen. setMovieBounds OSErr object self Sets the KRect* bounds¬ rectangular Rect region in which the movie appears when it is played. The movie will be scaled to fit the rectangle. Each movie has a default boundsRect that is the correct size for that movie. In general you are recommended not to change the boundsRect since the movie image will lose quality if it is resized. If you want the movie to appear in a different part of the screen other than the default boundsRect, you can use the offsetRect function to offset the boundsRect rectangle structure. (See the Imaging chapter for details of OffsetRect. ) getMovieBoundε void object self Sets the rect KRect *rect rectangle structure to have the same values as the rectangular region that defines the screen for the movie. setDisplayClipRgn void object self Sets the KRgnHandle clipRgn clipping region for the movie. The default clipping region on Sweatpea is the area that defines the movie bounds. Any part of the movie image that falls outside the clipping region will be clipped. So make sure that the clipping region and the movie's bounds rectangle overlap. getDisplayClipRgn KRgnHandle object self Returns the clipping region for the movie. pointlnMovie KBoolean object self Returns true KPoint point if the point is in the region where the movie will play. Sound Volume ranges from -1 to +1. Higher values indicate louder volumes. A value of 1 is equivalent to the loudest volume that can be played on the player. Negative values indicate muted volume. That is, the MoviePlayer does not play any sound for movies or tracks with negative volume settings. However, the original volume level is retained as the absolute value of the volume setting. Many of these methods take a track argument, which is the number of the track. The first track is 1.0, the second track is 2 and so on. Argument Name Type Type/Class Argument Description setMovieVolume void object self Sets the volume long volume for the movie. getMovieVolume short object self Returns the volume of the movie. getPreferredVolume short object self Returns the default volume of the movie. setTrackVolume void object self Sets the volume long track of a track. A long volume track's volume is scaled by the movie's volume to produce the track's final volume. getTrackVolume short object self Returns the long track volume for a given track. setTrackPan void object self Sets the pan long track (balance) for a long pan track. getTrackPan short object self Returns the pan long track (balance) for a given track. Alternate Tracks Argument Name Type Type/Claεε Argument Deεcription getTrackCount short object self Returns the total number of tracks in the movie. getTrackMediaType long object self Returns the long track media type of track. setTrackEnabled void object self If enableOrNot long track is 1, the movie long enable¬ player enables OrNot the given track. If enableOrNot is 0, the movie player disables the given track. If a track is enabled it can be played. If it is disabled, it cannot be played. All tracks are enabled by default. getTrackEnabled KBoolean object self Returns 1 if long track the given track is enabled, or 0 if it is disabled. setLanguage void object self Specifies the long language language for a movie. The movie player examines the movie's alternate groups and selects and enables an appropriate track. If the player cannot find an appropriate track, it does not change the movie's language. εelectAlternateε void object self Causes the movie player to select appropriate tracks immediately. You can call this method even if you have disabled automatic track selection with the AutoAlternateε method. autoAlternates void object self If enable is 1, KBoolean enable enables automatic track selection by the movie player. If enable is 0, disables automatic track selection. When automatic track selection is enabled, the movie player immediately selects active tracks for the movie. getTrackLanguage short object self. Returns the long track language or region code of the given track. getTrackQuality short object self Returns a long track track's quality level value. The Movie Player uses this quality value to influence which track it selects to play on a given computer. The quality value indicates the pixel depths at which the track's media can be played. This even applies to sound media. The low-order 6 bits of the quality value correspond to specific pixel depths. If a bit is set to 1, the media can be played at the corresponding depth. More than one of these bits may be set to 1. The following bits are defined: bit 0 1 bit per pixel 5 bit 1 2 bits per pixel bit 2 4 bits per pixel bit 3 8 bits per pixel bit 4 16 bits per pixel bit 5 32 bits per pixel 10 In addition, bits 6 and 7 define the media's quality level. A value of 0 corresponds to the lowest quality level; a value of 3 corresponds to the highest quality level: mediaQualityDraft - Specifies the lowest quality 15 level. This constant sets bits 6 and 7 to a value of 10. mediaQualityNormal - Specifies an acceptable quality level. This constant sets bits 6 and 7 to a value of 1. 20 mediaQualityBetter - Specifies a higher quality level. This constant sets bits 6 and 7 to a value of 2. mediaQualityBest - Specifies the highest quality level. This constant sets bits 6 and 7 to a value of 25 3. Creation Information Argument Name Type Type/Class Argument Description getlnfo void object self Returns the movie's long* created creation date/time long* modified and the modification date/time. The timestamp indicates the number of seconds since January 1, 1904. getTracklnfo void object self Returns the specified long track track's creation long* created date/time and long* modified modification date/ time. The timestamp indicates the number of seconds since January 1, 1904. Appendix 6 Instance Methods on CallBack Subclasses Argument Name Type Type/Class Argument Description getClock object object CallBack Returns the clock to which this CallBack iε attached. callMeWhen void object CallBack Specifies the CallBack-Proc CallBack procedure to void Proc be called when *CallBack- the CallBack long ProcParam is activated, long flags and specifies Time-Record rateORline how and when CallBack- *timerec the CallBack Priority iε to be activated. dispose void object CallBack Disposes of the CallBack object. cancelCallBack void object CallBack Cancel the pending CallBack. The user must call dispose on the CallBack to dispose it. Appendix 7 Audio Stream Methods /* steam support */ readBlock gets a block of sound streamLength length of stream cursor current position pastEnd - returns boolean seekFromStart seek from beginning of media seekFromCursor - seek from current position /* Sample messages */ getSampleSize getSampleRate getSampleType getCompType getPackingType getNumFrames getNumChannels setDirection - forward or reverse getDirection parseSoundData - called to convert external formats to internal format co puteApparentSize - varies depending on sample size, compressed, etc. allocateBuf - buffer used for intermediate conversions deAllocateBuf setPreferredSampleType - type preferred by audio driver getPreferredSampleType setPreferredByteType getPreferredByteType /* Player methods */ setlnputStream - stream from which we get data getAudioRecord - pointer to properties playPrepare - gets stream ready for playback playUnprepare /* Clock methods */ setRate - rate determines buffer filling getRate askRate Appendix 8 Audio Channel Driver Methods getMaxBufSize - maximum buffer size for driver setPreferredSampleType - preferred sample type getPreferredSampleType (multiple possible) setPreferredByteSize getPreferredByteSize setSampleRate getSampleRate setPackingType getPackingType setSampleType getSampleType setSampleSize getSa pleSize getCompType resetCDXAFilter setCDXAFilter getCDXAFilter setPlayer the player this driver is connected to getPlayer setGain getGain getGainLeft getGainRight setPan getPan setChannelPtr getChannelPtr setRate getRate askRate computeVolume computes volume from gain and pan play playPrepare playUnprepare stop - operates like pause finished fillBuffer - buffer management bufferFilled

Claims: What is claimed is: 1. A system of the type including classes having variables and methods which are organized in an object oriented class inheritance hierarchy, said system comprising: a clock class including at least one method for returning a time value; and a player class including at least one method for causing at least a portion of a media stream to be played at said time value, wherein said player class inherits from said clock class. 2. A system of the type including classes having variables and methods which are organized in an object oriented class inheritance hierarchy, said system comprising: a clock class including at least one method for returning a time value; a player class including at least one method for causing at least a portion of a media stream to be played at said time value; a player object which is an instance of said player class, said player object including means for operating at a speed at least as fast as that of any other instance of said player class; a root clock including means for operating at a speed at least as fast as that of said player object; and wherein said player object is synchronized to said root clock.

Inventors: MALOUF FREDERICK L, NEUMANN ERIK R, MALOUF, FREDERICK, L., NEUMANN, ERIK, R.
Applicants: KALEIDA LABS INC, KALEIDA LABS, INC.
Application year: 1994
Main classification: G06F15
IPC codes: G06F17, G11B20, G11B27, H04N5, H04N7